Good luck with your choice.
Imho tank and dps dual-spec'd for duo healing would be better choice. Only because tank and heals are the two most demanding roles in dungeons, and three random dps'ers can make boxing those two jobs 10x harder. Or easier, but its a crapshoot with LFG. And macroing heals for random group members has always been bugged for me, but maybe you have better luck than I with stuff like that. Seriously though, good luck and keep us posted on how it's going.

p.s. I know my sig says I'm two-boxing tank/heals in RIFT right now, but I don't group unless there is a main healer besides my toons in the party, I don't want the responsibility LOL.